Pneumatic rubber tires are typically composed of a carcass of a ply construction where the carcass plies are composed of a rubber composition reinforced with continuous cords. Such cords may be composed of, for example, synthetic and/or natural filaments such as for example nylon, aramid, polyester and/or rayon filaments or may be composed of steel or coated steel filaments. Such rubber composition conventionally also contains a dispersion of reinforcing filler composed of particulate rubber reinforcing carbon black or a combination of rubber reinforcing carbon black and precipitated silica. The tire carcass conventionally supports a circumferential rubber tread which also contains a circumferential belt ply between the tire carcass and tread composed of, for example, a continuous cord reinforcement composed of, for example, a filamentary steel cord.
Such cord reinforced tire carcass plies and belt plies are well known to those having skill in such art.
Sometimes, tires having a carcass composed of split carcass plies have been proposed to provide a beneficial tire carcass construction such as, for example, a reduction on tire weight and cost. For example, see U.S. Pat. No. 7,017,635 particularly its FIGS. 7 and 9, U.S. Pat. Nos. 6,913,052, 6,883,571, 6,883,570 and 6,305,452 and European Patent Publication No. 916 522.
In said U.S. Pat. No. 7,017,635, a tire carcass composed of cord reinforced split plies is presented with a central ply spanning the gap between the split plies to abridge and join the split ply ends.
In FIG. 9 of U.S. Pat. No. 7,017,635, a tire is depicted with a carcass comprised of cord-reinforced split radial plies (17a) and (17b) with their ply ends spaced apart from each other with an overlying belt ply (24) and, also, an additional flat ply (50) positioned below the split plies (17a) and (17b) and thereby below the belt ply (24) and spanning the gap between the split plies.
For this invention, it is proposed to provide a tire with cord-reinforced split radial plies having their split ply ends abridged and joined by at least one circumferential central rubber layer which abridges (and thereby joins) the split ply ends by overlapping and/or underlapping the split ply ends. The central rubber layer contains a dispersion of macro and/or micro reinforcement. Optionally, said central rubber layer may also contain continuous cord reinforcement.
A significant aspect of such abridging rubber layer, Which spans the gap between the split carcass ends, is considered herein to be the inclusion of macro and micro reinforcement in its rubber composition. This is considered herein to be significant in a sense of simplifying the tire manufacturing process through the elimination of the calendering procedure for the preparation of rubber coated ply cords.
A further significant aspect of such abridging rubber layer, which spans the gap between the split carcass ends, is considered herein to be an optional additional inclusion of continuous cord reinforcement in its rubber composition. This is considered herein to be significant in a sense of further enhancing the reinforcing characteristics of the center ply, hence enhancing the performance of the tire.
The split ply tire carcass is comprised of at least two cord reinforced carcass plies having their ply ends spaced apart in the crown portion (central portion) of the tire carcass. The said carcass ply ends are joined by at least one central rubber layer which abridges and overlaps and/or underlaps the said carcass ply ends.
For example, the central rubber layer abridges the gap between the split carcass ends by being positioned radially outward from, and thereby overlapping and joining the carcass split ply ends.
For a further example, the central rubber layer abridges (spans) the gap between the split carcass ends by being positioned radially inwardly from, and thereby underlapping and joining, the carcass split ply ends.
For an additional example, the two central rubber layers, namely a first and second central rubber layer, abridge the gap between the split carcass ends wherein the first central rubber layer is positioned radially outward from, and thereby overlapping and joining, the carcass split ply ends and the second central rubber layer is positioned radially inward from, and thereby underlapping and joining, the carcass split ply ends. Optionally said first and second central rubber layers are in contact with each other to form a unitized configuration within the gap between the split carcass ends.
The central rubber layer composition is comprised of a rubber composition which contains a dispersion of macro and/or micro reinforcing fillers either to the exclusion of internal continuous cord reinforcement or in combination with internal continuous cord reinforcement.
Such macro reinforcement is, for example, comprised of short synthetic and/or natural filaments including cords comprised of a plurality of such filaments. Representative of such synthetic and/or natural filaments are, for example, nylon, aramid, polyester, glass, steel, coated steel and/or rayon filaments.
Such micro reinforcement is, for example, comprised of at least one polymer selected from syndiotactic polybutadiene, and a poly alpha-olefin such as for example, ultra high molecular weight polyethylene (UHMWPE), polypropylene, polybutene and poly 4-methyl-1-pentene, in addition to at least one of particulate rubber reinforcing carbon black and synthetic amorphous precipitated silica.
A significant aspect of such abridging (spanning the gap between the split carcass ply ends) central rubber layer is considered herein as providing support to the gap between the split carcass ply ends in a sense of promoting supportive durability to the split carcass ply (e.g. promoting a continuation of the carcass ply across the gap between its split ply ends) and, further to promote additional strength for the gap between the carcass split ply ends with an inclusion of continuous cord reinforcement within the macro and/or micro reinforced central rubber layer.
In the description of this invention, the terms “rubber” and “elastomer” where used herein, are used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, where used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients” and the term “compound” relates to a “rubber composition” unless otherwise indicated. Such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated.
The term “melting point”, or “MP”, of a polymer refers to a melting point of a polymer determined by DSC (differential scanning calorimeter) at a heating rate of 10° C. per minute, an analytical procedure well known to those having skill in such art.